is available to cross the resonance barrier in waves of larger \ R *, it can be advantageous 

 to extend the supercritical range as far as possible by increasing natural periods. The 



H S 



means leading to this goal are large — , large CT = — , large mass factors. The penalty 



L a 



which one has to pay consists in a pronounced deterioration of qualities in the resonance 

 condition [10]. 



3.3. Wetness 



Relative motions of the ship with respect to the water surface rather than the 

 absolute motions, determine wetness. Naturally, the corresponding equations should 

 be used, although this so far has not been done in general. 



A lot of experimenting has been carried out on wetness. Using the standard 

 h 1 



steepness ratio — = — , very unfavorable conditions are obtained in larger waves in 

 A 20 



the neighborhood of synchronism. 



For a better understanding of the matter it is advisable to test models at lower 

 steepness ratios where the assumption of linearity still holds and comparison with the 

 existing theory is justified. 



Again, only a small amount of systematic work based on such comparison has 

 been performed. Szebehely [52] found that the present theory yields a useful guide 

 for slamming investigations but that quantitative agreement between results of meas- 

 urements and calculations is frequently lacking. Vladimirov [67] improved the predic- 

 tion of wetness phenomena by adding wave effects, calculated for the speed of advance 

 in calm water, to the surface of the sea. The theoretical determination of phase angles 

 which is decisive in this kind of research is not too reliable. Further, the distortion 

 of waves caused by the advancing and oscillating ship cannot yet be calculated by our 

 present elementary approach. Earlier inspiring attempts by Kreitner, are based on 

 rather arbitrary assumptions. 



In the subcritical range the relative motion of the ship with respect to the 

 corrugated water surface improves at large A*. The question arises as to what criteria 

 should be used for activated pitch stabilization — a problem which becomes urgent at 

 present after reasonable suggestions have been made some twenty-five years ago to use 

 fins. 



An increase in damping tends to tie up the ship with the wave surface in larger 

 waves which appears to be a reasonable answer in the subcritical zone. In fact, for 

 a phase angle e < 90° it can be shown that the most favorable results with respect to 



wetness can be obtained at the bow when the linear motion amplitude Z mbow ~ r m cos e. 

 When £ > 90° the best answer is "horizontalization" i.e., ip m — O. This seems to settle 

 the question. 



4. Hydrodynamic Impacts 



At present, this topic has been so frequently discussed [4], [5], [52] that we can 

 restrict ourselves to few remarks only. 



The following form characteristics appear desirable to avoid hydrodynamic 

 impacts: 



1 . high rise of floor at the ends, especially at the bow, 



2. sufficient draft, again primarily at the bow, 



3. moderate angles of entrance at and above the waterline, 



4. moderate, not excessive, flare in the forebody (St. Vincent), 



5. to combine conditions 3. and 4. a clipper stern is advantageous, 



6. high freeboard and sheer, including a forecastle to keep the deck free from 

 impacts by green water. The forecastle should be designed with respect to 

 horizontal impacts (for example, whale-back). 



90 



